The manner of prior incorporation of photographically useful agents in a photographic light-sensitive material to fully achieve the effects of the agents differs from the manner in which they are used in processing solutions. For instance, photographic agents of the kind which cannot withstand long range storage in processing solutions because of their liability to decomposition under acid-alkaline or oxidation-reduction conditions can be utilized effectively and at the same time, the composition of a processing solution can be simplified to facilitate the preparation thereof. Further, in processing a light-sensitive material, it becomes feasible for a desired photographic agent to fulfill its function at a desired time and/or at a desired place, that is to say, only in a specific layer or layers in the vicinity thereof where the light-sensitive material has a multilayer structure, or for a desired photographic agent to be present in such an amount as to vary as a function of silver halide development. However, if the photographic agent is added to a photographic material in an active form, it undergoes reactions with other components present in the photographic light-sensitive material or decomposes under the influence of heat or oxygen during storage prior to processing. Therefore, it becomes impossible to achieve fully the expected capabilities at the time of processing. One solution to this problem is a method in which a photographic agent is converted into a substantially inactive form by blocking the active group, that is, a precursor thereof, and then the precursor is added to a photographic light-sensitive material. When the useful photographic agent is a dye, a functional group having a great effect on spectral absorption of the dye is blocked and, thereby, its spectral absorption is shifted to the shorter or the longer wavelength side. Under this circumstance, even if the blocked dye is also present in a silver halide emulsion layer with a spectral sensitivity in the wavelength region corresponding to the spectral absorption of the original dye, a lowering of sensitivity due to the so-called filter effect does not occur. Therefore, it can be used advantageously. When the photographically useful agent is an antifoggant or a development inhibitor, blocking of the active group can offer many advantages, e.g., desensitization due to adsorption onto light-sensitive silver halide grains and formation of silver salts upon storage can be inhibited, and at the same time, through timely release of such photographic agents, fog can be reduced without impairing photographic speed, fog arising from overdevelopment can be stopped at a desired time, and so on. When the photographically useful agent is a developer, an auxiliary developer or a fogging agent, blocking the active group or the adsorptive group can offer the advantages that various photographically adverse effects due to conversion into semiquinones or oxidants through air oxidation on storage can be prevented, or injection of electrons into silver halides can be prevented from occurring during storage. Thereby, generation of fog nuclei can be inhibited. This results in the realization of stable processing, and the like. When the photographically useful agent is a bleach accelerator or a bleach-fix accelerator, blocking the active group can offer the advantages that in storing the light-sensitive material, reactions with other components present together with such an agent can be suppressed, while in processing it, the expected ability can be brought into full play upon removal of the blocking group at the time needed. In the present invention the above described active group, functional group and adsorptive group are generally referred to as active group.
As described above, to use a photographic agent in the form of a precursor thereof turns out to be an extremely effective means of freely achieving the ability of the photographic agent. However, precursors thereof have very severe requirements for practical use. That is, they must satisfy two contradictory requirements; one is ensuring stable presence of the precursor under a storage condition, and the other is ensuring rapid and highly efficient release of the photographic agent by removal of the blocking group at a desired time upon processing.
Several techniques for blocking photographic agents are already known. For example, well known techniques involve utilization of a blocking group such as an acyl group, a sulfonyl group or the like, as described in Japanese Patent Publication No. 44805/72 (corresponding to U.S. Pat. No. 3,615,617); utilization of a blocking group which releases a photographic agent due to the so-called reverse Michael's reaction, as described in Japanese Patent Publication Nos. 39727/79 (corresponding to U.S. Pat. No. 3,674,478), 9696/80 (corresponding to U.S. Pat. No. 3,791,830) and 34927/80 (corresponding to U.S. Pat. No. 4,009,029); utilization of a blocking group which releases a photographic agent by an intramolecular electron transfer accompanying the production of quinone methide or the analogues thereof, as described in U.S. Pat. No. 4,350,754, Japanese Patent Publication No. 39727/79, and Japanese Patent Application (OPI) Nos. 135944/82, 135945/82 and 136640/82 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"); utilization of the intramolecular ring closure reaction described in Japanese Patent Application (OPI) No. 53330/80 (corresponding to U.S. Pat. No. 4,310,612); utilization of the cleavage of a 5- or 6-membered ring described in Japanese Patent Application (OPI) Nos. 76541/82 (corresponding to U.S. Pat. No. 4,335,200), 135949/82 and 179842/82; and so on.
However, photographic agents blocked using these known techniques have the disadvantages that, for example, some precursors which are stable under storage conditions release photographic agents too slowly at the time of processing and, therefore, they require the processing under high alkalinities of a pH of 12 or above, some precursors which have sufficiently high release speeds at the time of processing under mild conditions of a pH of 9 to 11 decompose slowly under storage conditions, thereby impairing their function as a precursor, some precursors which allow little latitude in controlling the release speed at the time of processing require a very narrow pH range for effecting the processing, and so on.